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LED Optoisolator Cell-Battery Management V/I Regulator Tip
Im working on a cell-battery tray for breadboarding electronics, using dual six packs of Nickle Metal Hydride AA cells.
Managing the 5 volt 1A regulator with two 68V Zeners back 2 back across the output protects the semiconductors in the regulator up to 68V in either polarity.
(Relays on breadboards can generate micro-power spikes in excess of 1KV when the coil is interupted), good insurance.
The _LED optoisolator_ input LED is on the emitter of a large NPN (TIP31) and is passed in parallel with a 56 Ohm 3 Watt.
Keeping the emitter at (6 * 1.2V) = 7.2V regulates the maximum voltage at the top of the cell battery trays, while the 56 Ohm resistor limits maximum current if the cells are found in a very discharged state.
If the drop across the resistor is > 2.78V, the isolator CE junction saturates and can pull down the TIP31 base in parallel with a 10K resistor.
Limiting the maximum current from the emitter to (2.78V/56 Ohms) to ~50 mAmps, protects the nickle-metal cells from overcharging, both in voltage and current.
Im working on a cell-battery tray for breadboarding electronics, using dual six packs of Nickle Metal Hydride AA cells.
Managing the 5 volt 1A regulator with two 68V Zeners back 2 back across the output protects the semiconductors in the regulator up to 68V in either polarity.
(Relays on breadboards can generate micro-power spikes in excess of 1KV when the coil is interupted), good insurance.
The _LED optoisolator_ input LED is on the emitter of a large NPN (TIP31) and is passed in parallel with a 56 Ohm 3 Watt.
Keeping the emitter at (6 * 1.2V) = 7.2V regulates the maximum voltage at the top of the cell battery trays, while the 56 Ohm resistor limits maximum current if the cells are found in a very discharged state.
If the drop across the resistor is > 2.78V, the isolator CE junction saturates and can pull down the TIP31 base in parallel with a 10K resistor.
Limiting the maximum current from the emitter to (2.78V/56 Ohms) to ~50 mAmps, protects the nickle-metal cells from overcharging, both in voltage and current.
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Nevada
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Re: LED Optoisolator Cell-Battery Management
Sat, October 10, 2009 - 5:41 PMA reverse diode is usually put across the relay coil to prevent the spike from the inductive kickback. Cheaper than the dual zeners. Some relays already have them built in. -
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Re: LED Optoisolator Cell-Battery Management
Sun, October 11, 2009 - 4:59 AMYes, a run-of-the-mill el cheapo silicon diode will do the trick. It doesn't have to be particularly large, because even though it will be bypassing large voltages, they will be very brief pulses, and the diode will clamp the voltage down to around 600mV or so. Just pop it in right across the relay coil with the cathode on the positive leg and the anode on the negative. It will keep things nice and simple, and put you to where you don't have to ruggedize the rest of the rig so much.
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